Pharmaceutical Biotechnology

1. Pharmaceutical Biotechnology 4.The Drug development process Dr. Tarek El-Bashiti Assoc. Prof. of Biotechnology

2. In this chapter, the life history of a successful drug will be outlined (summarized in Figure 4.1). • A number of different strategies are adopted by the pharmaceutical industry in their efforts to identify new drug products. • These approaches range from random screening of a wide range of biological materials to knowledge-based drug identification.

3. An overview of the life history of a successful drug. Patenting of the product is usually also undertaken, often during the initial stages of clinical trial work.

4. Clinical trials are required to prove that the drug is safe and effective when administered to human patients, and these trials may take 5 years or more to complete. • Once the drug has been characterized, and perhaps early clinical work is underway, the drug is normally patented by the developing company in order to ensure that it receives maximal commercial benefit from the discovery. • Post-marketing surveillance is generally undertaken, with the company being obliged to report any subsequent drug-induced side effects/adverse reactions.

5. Discovery of biopharmaceuticals • The discovery of virtually all the biopharmaceuticals discussed in this text was a knowledge-based one. • Simple examples illustrating this include the use of insulin to treat diabetes and the use of GH to treat certain forms of dwarfism (Chapter 11). • The underlining causes of these types of disease are relatively straightforward, in that they are essentially promoted by the deficiency/absence of a single regulatory molecule.

6. Other diseases, however, may be multifactorial and, hence, more complex. • Examples include cancer and inflammation. • Nevertheless, cytokines, such as interferons and interleukins, known to stimulate the immune response/regulate inflammation, have proven to be therapeutically useful in treating several such complex diseases (Chapters 8 and 9). • The physiological responses induced by the potential biopharmaceutical in vitro (or in animal models) may not accurately predict the physiological responses seen when the product is administered to a diseased human.

7. For example, many of the most promising biopharmaceutical therapeutic agents (e.g. virtually all the cytokines, Chapter 8), display multiple activities on different cell populations. • This makes it difficult, if not impossible, to predict what the overall effect administration of any biopharmaceutical will have on the whole body, hence the requirement for clinical trials. • In other cases, the widespread application of a biopharmaceutical may be hindered by the occurrence of relatively toxic side effects (as is the case with tumour necrosis factor α(TNF-α, Chapter 9).

8. Finally, some biomolecules have been discovered and purified because of a characteristic biological activity that, subsequently, was found not to be the molecule’s primary biological activity. • TNF-α again serves as an example. • It was first noted because of its cytotoxic effects on some cancer cell types in vitro. • Subsequently, trials assessing its therapeutic application in cancer proved disappointing due not only to its toxic side effects, but also to its moderate, at best, cytotoxic effect on many cancer cell types in vivo.

9. The impact of genomics and related technologies upon drug discovery • The term ‘genomics’ refers to the systematic study of the entire genome of an organism. • Its core aim is to sequence the entire DNA complement of the cell and to map the genome arrangement physically (assign exact positions in the genome to the various genes/non-coding regions). • Modern sequencing systems can sequence thousands of bases per hour.

10. By early 2006 some 364 genome projects had been completed (297 bacterial, 26 Archaeal and 41 Eucaryal, including the human genome) with in excess of 1000 genome sequencing projects ongoing. • From a drug discovery/development prospective, the significance of genome data is that they provide full sequence information of every protein the organism can produce. • This should result in the identification of previously undiscovered proteins that will have potential therapeutic application, i.e. the process should help identify new potential biopharmaceuticals.

11. The greatest pharmaceutical impact of sequence data, however, will almost certainly be the identification of numerous additional drug targets. • The majority of such targets are proteins (mainly enzymes, hormones, ion channels and nuclear receptors). • Additionally, present in the sequence data of many human pathogens is sequence data of hundreds, perhaps thousands, of pathogen proteins that could serve as drug targets against those pathogens (e.g. gene products essential for pathogen viability or infectivity). • The focus of genome research, therefore, is now shifting towards elucidating the biological function of these gene products, i.e. shifting towards ‘functional genomics’.

12. In the context of genomics, gene function is assigned a broader meaning, incorporating not only the isolated biological function/activity of the gene product, but also relating to: • where in the cell that product acts and, in particular, what other cellular elements does it influence/interact with; • how do such influences/interactions contribute to the overall physiology of the organism.

13. The assignment of function to the products of sequenced genes can be pursued via various approaches, including: • sequence homology studies; • phylogenetic profiling; • Rosetta stone method; • gene neighbourhood method; • knockout animal studies; • DNA array technology (gene chips); • proteomics approach; • structural genomics approach.

14. With the exception of knockout animals, these approaches employ, in part at least, sequence structure/data interrogation/comparison. • Phylogenetic profiling entails establishing a pattern of the presence or absence of the particular gene coding for a protein of unknown function across a range of different organisms whose genomes have been sequenced. • If it displays an identical presence/absence pattern to an already characterized gene, then in many instances it can be inferred that both gene products have a related function.

15. The Rosetta stone approach is dependent upon the observation that sometimes two separate polypeptides (i.e. gene products X and Y) found in one organism occur in a different organism as a single fused protein XY. • In such circumstances, the two protein parts (domains), X and Y, often display linked functions. • Therefore, if gene X is recently discovered in a newly sequenced genome and is of unknown function but gene XY of known function has been previously discovered in a different genome, then the function of the unknown X can be deduced.

16. The gene neighbourhood method It depends upon the observation that two genes are likely to be functionally linked if they are consistently found side by side in the genome of several different organisms. • Knockout animal studies, in contrast to the above methods, are dependent upon phenotype observation. • By generation and study of mice in which a specific gene has been deleted. • Phenotypic studies can sometimes yield clues as to the function of the gene knocked out.

17. Gene chips: (DNA arrays, oligonucleotide arrays, chip arrays or, chips) • Although sequence data provide a profile of all the genes present in a genome, they give no information as to which genes are switched on (transcribed) and, hence, which are functionally active at any given time/under any given circumstances. • For example, if a particular mRNA is only produced by a cancer cell, that mRNA (or, more commonly, its polypeptide product) may represent a good target for a novel anti-cancer drug. • Standard gridding robots can put on up to 250 000 different short oligonucleotide probes or 10 000 full-length cDNA sequences per square centimetre of surface. • RNA can be extracted from a cell and probed with the chip. Any complementary RNA sequences present will hybridize with the appropriate immobilized chip sequence (Figure 4.2).

19. Proteomics • Although virtually all drug targets are protein based, the inference that protein expression levels can be accurately (if indirectly) detected/measured via DNA array technology is a false one, as: • mRNA concentrations do not always directly correlate with the concentration of the mRNA-encoded polypeptide; • a significant proportion of eukaryote mRNAs undergo differential splicing and, therefore, can yield more than one polypeptide product (Figure 4.3). • Therefore, protein-based drug leads/targets are often more successfully identified by direct examination of the expressed protein complement of the cell, i.e. its proteome.

21. Structural genomics: • The basic approach to structural genomics entails the cloning and recombinant expression of cellular proteins, followed by their purification and three-dimensional structural analysis (X-ray crystallography or NMR). • For example, in excess of 50 different structures of ‘insulin’ have been deposited (e.g. both native and mutated/engineered forms from various species, as well as insulins in various polymeric forms and in the presence of various stabilizers and other chemicals). • It may prove ultimately feasible to predict protein function if its structure is known, and vice versa

22. Pharmacogenetics • Pharmacogenetics correlating specific gene DNA sequence information (specifically sequence variations) to drug response. • Different people respond differently to any given drug, even if they present with essentially identical disease symptoms. • Optimum dose requirements, for example, can vary significantly. • Furthermore, not all patients respond positively to a specific drug (e.g. IFN-β is of clinical benefit to only one in three multiple sclerosis patients. • The range and severity of adverse effects induced by a drug can also vary significantly within a patient population base, genetic variation amongst individuals remains the predominant factor.

23. Although all humans display almost identical genome sequences, some differences are evident. • The most prominent widespread-type variations amongst individuals are known as single nucleotide polymorphisms (SNPs, sometimes pronounced ‘snips’). • In this context, the protein product could, for example, be the drug target or perhaps an enzyme involved in metabolizing the drug. • By identifying and comparing SNP patterns from a group of patients responsive to a particular drug with patterns displayed by a group of unresponsive patients, it may be possible to identify specific SNP characteristics linked to drug efficacy.

24. This could usher a new era of drug therapy where drug treatment could be tailored to the individual patient. • A (distant) futuristic scenario could be visualized where all individuals could carry chips encoded with SNP details relating to their specific genome, allowing medical staff to choose the most appropriate drugs to prescribe in any given circumstance.

25. Initial product characterization • The physicochemical and other properties of any newly identified drug must be extensively characterized prior to its entry into clinical trials. • A prerequisite to such characterization is initial purification of the protein. • Purification to homogeneity usually requires a combination of three or more high-resolution chromatographic steps.

26. Figure 4.5: Task tree for the structural characterization of a therapeutic protein.

27. In addition to the studies listed in Figure 4.5, stability characteristics of the protein with regard to e.g. temperature, pH and incubation with various potential excipients are studied. • Such information is required in order to identify a suitable final product formulation, and to give an early indication of the likely useful shelf-life of the product.

28. Patenting • The discovery and initial characterization of any substance of potential pharmaceutical application is followed by its patenting. • Thus, patenting may not take place until preclinical trials and phase I clinical trials are completed. • Patenting, once successfully completed, does not grant the patent holder an automatic right to utilize/sell the patented product; first, it must be proven safe and effective in subsequent clinical trials, and then be approved for general medical use by the relevant regulatory authorities.

30. Delivery of biopharmaceuticals • To date, the vast majority of biopharmaceuticals approved for general medical use are administered by direct injection (i.e. parenterally) usually by intravenous (i.v.), subcutaneous (s.c., i.e. directly under the skin) or intramuscular (i.m., i.e. into muscle tissue) routes. • Amongst the few exceptions to this parenteral route are the enzyme DNase, used to treat cystic fibrosis, and platelet-derived growth factor (PDGF), used to treat certain skin ulcers. • In fact, in each case the delivery system delivers the biopharmaceutical directly to its site of action (DNase is delivered directly to the lungs via aerosol inhalation, and PDGF is applied topically, i.e. directly on the ulcer surface, as a gel).

31. Alternative potential delivery routes include oral, nasal, transmucosal, transdermal or pulmonary routes. • Although such routes have proven possible in the context of many drugs, routine administration of biopharmaceuticals by such means has proven to be technically challenging. • Obstacles encountered include their high molecular mass, their susceptibility to enzymatic inactivation and their potential to aggregate.

32. 1.Oral delivery systems • Oral delivery is usually the preferred system for drug delivery, owing to its convenience and the high level of associated patient compliance generally attained. • Biopharmaceutical delivery via this route has proven problematic for a number of reasons: • Inactivation due to stomach acid. Virtually all biopharmaceuticals are acid labile and are inactivated at low pH values. • Inactivation due to digestive proteases.

33. 3. Their (relatively) large size and hydrophilic nature renders difficult the passage of intact biopharmaceuticals across the intestinal mucosa. 4. Orally absorbed drugs are subjected to first-pass metabolism. Upon entry into the bloodstream, the first organ encountered is the liver, which usually removes a significant proportion of absorbed drugs from circulation. • Strategies pursued to improve bioavailability include physically protecting the drug via encapsulation and formulation as microemulsions/microparticulates, as well as inclusion of protease inhibitors and permeability enhancers

34. Microcapsules/spheres utilized have been made from various polymeric substances, including cellulose, polyvinyl alcohol, polymethylacrylates and polystyrene. • Delivery systems based upon the use of liposomes and cyclodextrin-protective coats have also been developed. • Despite intensive efforts, however, the successful delivery of biopharmaceuticals via the oral route remains some way off.

35. 2.Pulmonary delivery • Delivery via the pulmonary route moved from concept to reality in 2006 with the approval of Exubera, an inhalable insulin product. • Although the lung is not particularly permeable to solutes of low molecular mass (e.g. sucrose or urea), macromolecules can be absorbed into the blood via the lungs surprisingly well. • In fact, pulmonary macromolecular absorption generally appears to be inversely related to molecular mass, up to a mass of about 500 kDa.

36. Although not completely understood, such high pulmonary bioavailability may stem from: • the lung’s very large surface area; • their low surface fluid volume; • thin diffusional layer;

37. Additional advantages associated with the pulmonary route include: • the avoidance of first-pass metabolism; • the availability of reliable, metered nebulizer-based delivery systems capable of accurate dosage • delivery, either in powder or liquid form; • levels of absorption achieved without the need to include penetration enhancers which are generally too irritating for long-term use. • Although the molecular details remain unclear, this absorption process appears to occur via one of two possible means: transcytosis or paracellular transport (Figure 4.6).

39. 3.Nasal, transmucosal and transdermal delivery systems • A nasal-based biopharmaceutical delivery route is considered potentially attractive as: • It is easily accessible; • Nasal cavities are serviced by a high density of blood vessels; • Nasal microvilli generate a large potential absorption surface area; • Nasal delivery ensures the drug bypasses first-pass metabolism.

40. However, the route does display some disadvantages, including: • Clearance of a proportion of administered drug occurs due to its deposition upon the nasal mucous blanket, which is constantly cleared by ciliary action; • The existence of extracellular nasal proteases/peptidases; • Low uptake rates for larger peptides/polypeptides.

41. Research efforts also continue to explore mucosal delivery of peptides/proteins via the buccal, vaginal and rectal routes. • Again, bioavailabilities recorded are low, with modest increases observed upon inclusion of permeation enhancers. • Additional barriers also exist relating, for example, to low surface areas, relatively rapid clearance from the mouth (buccal) cavity and the cyclic changes characteristic of vaginal tissue. • Various strategies have been adopted in an attempt to achieve biopharmaceutical delivery across the skin (transdermal systems).

42. Preclinical studies • In order to gain approval for general medical use, the quality, safety and efficacy of any product must be demonstrated. • Demonstration of conformance to these requirements, particularly safety and efficacy, is largely attained by undertaking clinical trials. • However, preliminary data, especially safety data, must be obtained prior to the drug’s administration to human volunteers. • Regulatory authority approval to commence clinical trials is based largely upon preclinical pharmacological and toxicological assessment of the potential new drug in animals.

43. Such preclinical studies can take up to 3 years to complete, and at a cost of anywhere between US$10 million and US$30 million. • On average, approximately 10 per cent of potential new drugs survive preclinical trials. • The range of studies generally undertaken with regard to traditional chemical-based pharmaceuticals is summarized in Table 4.2. • Most of these tests are equally applicable to biopharmaceutical products.

45. Pharmacokinetics and pharmacodynamics • Pharmacology may be described as the study of the properties of drugs and how they interact with/affect the body. • Within this broad discipline exist (somewhat artificial) subdisciplines, including pharmacokinetics and pharmacodynamics. • Pharmacokinetics relates to the fate of a drug in the body, particularly its ADME, i.e. its absorption into the body, its distribution within the body, its metabolism by the body, and its excretion from the body. • Generally, ADME studies are undertaken in two species, usually rats and dogs, and studies are repeated at various different dosage levels in both males and females.

46. If initial clinical trials reveal differences in human versus animal model pharmacokinetic profiles, additional pharmacokinetic studies may be necessary using primates. • Pharmacodynamic studies deal more specifically with how the drug brings about its characteristic effects. • Emphasis in such studies is often placed upon how a drug interacts with a cell/organ type, the effects and side effects it induces, and observed dose–response curves. • Bioavailability relates to the proportion of a drug that actually reaches its site of action after administration.

47. Protein pharmacokinetics • A prerequisite to pharmacokinetic/pharmacodynamic studies is the availability of a sufficiently selective and sensitive assay. • Specific proteins are usually detected and quantified either via immunoassay or bioassay. • Additional analytical approaches occasionally used include liquid chromatography (e.g. HPLC) or the use of radioactively labelled protein. • Whole-body distribution studies are undertaken mainly in order to assess tissue targeting and to identify the major elimination routes.

48. The metabolism/elimination of therapeutic proteins occurs via processes identical to those pertaining to native endogenous proteins. • Although the therapeutic protein may be subject to limited proteolysis in the blood, extensive and full metabolism occurs intracellularly, subsequent to product cellular uptake. • Clearance of protein drugs from systemic circulation commences with passage across the capillary endothelia. • The rate of passage depends upon the protein’s physicochemical properties (e.g. mass and charge). • Final product excretion is, in the main, either renal and/or hepatic mediated.

49. Many proteins of molecular mass <30 kDa are eliminated by the kidneys via glomerular filtration. • In addition to size, filtration is also dependent upon the protein’s charge characteristics. • After initial filtration many proteins are actively reabsorbed (endocytosed) by the proximal tubules and subjected to lysosomal degradation, with subsequent amino acid reabsorption. • Thus, very little intact protein actually enters the urine. • Uptake of protein by hepatocytes can occur via one of two mechanisms: • receptor-mediated endocytosis or (b) non-selective pinocytosis, again with subsequent protein proteolysis.